1. Field of the Invention
This invention relates to a polarographic catheter-shaped probe for determining the analytical data of biological fluids of humans, of animals, or of plants, and having a cathode, an anode and an electrolyte connecting the two, which are surrounded by a sheath closed by a flexible membrane impermeable to ions in the region of the cathode tip but permeable to gases.
2. Description of the Prior Art
Already known from U.S. Pat. No. 3,528,403 is a sensing probe in which the cathode and the anode are positioned parallel to each other within a plastic structural member and are surrounded by a plastic sheath having a gas-permeable membrane in the region of the tip of the cathode. The electrolyte connecting the cathode with the anode is located in a cavity in the region of the tip of the plastic sheath. This probe is incorporated into a catheter shaft when measurements are made.
In another known sensing probe, disclosed in U.S. Pat. No. 3,758,398, the cathode is concentrically surrounded by the anode, and both are held inside a unit. A cap supporting a gas permeable membrane is filled with electrolyte and is then screwed onto the unit supporting the electrodes.
In U.S. Pat. No. 3,259,124 is disclosed another prior art probe in catheter form. This probe is constructed for taking measurements in the human body and has the electrode arrangement in the front end of a flexible tube closed by a gas-permeable membrane. The electrode arrangement is formed by two concentrically arranged electrodes insulated with respect to each other and extending to the tip of the probe, their conducting relationship established through an electrolyte also provided in the tip of the probe.
Since for all prior art catheter-shaped probes the anode and the cathode are arranged in the region of the tip of the probe and, accordingly, the reservoir for the electrolyte is also located in this region, extreme miniaturization of the primary element becomes very problematical, making great demands with respect to precision during the manufacturing process. The diameters of previously available catheter probes cannot be reduced below 1.5 mm. But this means that such probes can hardly be used for measurements on particularly small living creatures, because these dimensions are still too great for introduction into the fine channels of body fluids.